Selective firing apparatus

ABSTRACT

Improved apparatus for selectively firing charges in a well penetrating subterranean formations characterized by a plurality of discrete and separable guns; each carrying, in addition to its predetermined number of charges, a multi-deck stepping switch for connecting the charges with the firing conductor in sequence within each gun, the stepping switch of each lower gun having an electrical connection with the stepping relay of the stepping switch of the next higher gun such that the next higher gun is stepped from an isolating contact onto its first charge after, and only after, all of the charges in the lower gun have been fired. Appropriate unidirectional conduction means are provided to pass current of a first polarity for firing the charges; pass current of a second polarity for stepping onto the next charge; and to isolate electrically, lower guns such that they will not cause a malfunction even if their conductors should become grounded. An electrical interconnection is provided on the bottom gun such that its stepping switch may be stepped from its isolating contact by current of the second polarity. Specific structural and preferred embodiments are also disclosed.

waited States Patent [191 Halimark Oct. 30, 1973 l l SELECTIVE FIRINGAPPARATUS Bobby J. Hallmark, Fort Worth, Tex.

[73] Assignee: Gearhart-Owen Industries, Inc.,

Fort Worth, Tex.

[22] Filed: Sept. 30, 1971 [21] Appl. No.: 185,035

[75] Inventor:

Primary ExaminerBenjamin A. Borchelt Assistant Examiner-J. V. DoramusAttorney-Wm. T. Woofford et al.

[57] ABSTRACT Improved apparatus for selectively firing charges in awell penetrating subterranean formations characterized by a plurality ofdiscrete and separable guns; each carrying, in addition to itspredetermined number of charges, a multi-deck stepping switch forconnecting the charges with the firing conductor in sequence within eachgun, the stepping switch of each lower gun having an electricalconnection with the stepping relay of the stepping switch of the nexthigher gun such that the next higher gun is stepped from an isolatingcontact onto its first charge after, and only after, all of the chargesin the lower gun have been fired. Appropriate unidirectional conductionmeans are provided to pass current of a first polarity for firing thecharges; pass current of a second polarity for stepping onto the nextcharge; and to isolate electrically, lower guns such that they will notcause a malfunction even if their conductors should become grounded. Anelectrical interconnection is provided on the bottom gun such that itsstepping switch may be stepped from its isolating contact by current ofthe second polarity. Specific structural and preferred embodiments arealso disclosed.

7 Claims, 4 Drawing Figures PAIENIEDumo I973 31683108 SHEET 1 0F 2SELECTOR 0.0. VOLTAGE SWITCH SUPPLY Maw A TTORNEYS SELECTIVE FIRINGAPPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to apparatus for detonation of explosive charges at alocation remote from a control location. More particularly, it relatesto well perforating apparatus for selectively firing a pluraltiy ofelectrically detonable perforating means individually.

2. Description of the Prior Art As noted in US. Pat. No. 3,126,964, ithas been the usual practice to employ a perforating gun having amultiplicity of explosive charges positioned therealong andinterconnected by a line explosive, such as Primacord, for the purposeof detonating the explosive charges. The Primacord is detonated by anelectrically detonable squib disposed in the housing of the perforatinggun. The simultaneous detonaton of the line explosive and the explosiveperforating charges releases a tremendous amount of energy, frequentlydamaging the well casing. Moreover, to have a successful perforating jobwith the desired number of perforations, the preparation of the gun mustbe planned in advance so that the proper number of charges are employed.Also, the transportation of the gun with the charges electricallyconnected presented a hazard since stray currents could be induced; forexample, by static electricity or t by electromagnetic energyemanations, such as from television broadcasting towers.

The improvement in the invention described by LaRue in US. Pat. No.3,126,964 enabled firing the explosive charges individually in adownhole gun. Insofar as I am aware, however, the prior art has notprovided a plurality of gun means in which the charges in each gun couldbe selectively and individually fired and in which the next upper gunwould thereafter, and only thereafter, be armed so that it could befired. Particularly, the prior art has not provided perforatingapparatus incorporating a plurality of guns, each of the guns beingreadily prepared and assembled into the overall perforating apparatus atthe well site, thereby providing increased flexibility without thenecessity for elaborate pre-planning.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of awell installation and perforating apparatus in accordance with oneembodiment of this invention.

FIG. 2 is a partial side elevational view, partly cutaway, of themodular construction of the embodiment of FIG. 1 facilitating fieldassembly of the guns to do a desired perforating job.

FIG. 3 is a partial side elevational view, partly cutaway, illustratingthe apparatus for assembling the charge-containing subassemblies in agun in the embodiment of FIG. 1.

FIG. 4 is an electrical schematic diagram of the perforating apparatusin accordance with one embodiment of this invention.

DESCRIPTION OF PREFERRED EMBODIMENTS It is an object of this inventionto provide apparatus for selectively detonating from an operatinglocation a plurality of electrically detonable explosive charge meanslocated at a remote location by apparatus incorporating a plurality ofdiscrete and separable guns, each gun having a plurality of charges;means for firing the charges; and means for arming the next higher gunafter, and only after, all of the charges have been fired in the lowergun. It is a specific object of the invention to also provide, singly orin combination, and in addition to the foregoing object, unidirectionalconduction means to allow firing of the charges by a signal of a firstpolarity; stepping of the advancing means onto the respective charges bya signal of a second polarity; and electrical isolation so that a shortcircuit in a lower, previously fired gun will not adversely affectoperation of an upper gun.

It is also an object of this invention to provide modular constructionsuch that a plurality of guns containing the desired number of chargesand their firing means can be assembled at the well site for a highdegree of flexibility in effecting the desired perforating of wells,including the so-called pin point perforating.

Other objects will become apparent from the detailed descriptive matterhereinafter, particularly when taken in conjunction with the drawingsdelineated hereinbefore.

Referring to FIG. 1, borehole 11 extends from the earth s surface 13 toa productive subterranean formation 15. The borehole 11 has casing 17bonded to the wall of the borehole by a cement sheath 19 in conventionalmanner. Perforating apparatus is illustrated emplaced in the well forselectively detonating, from the surface, a plurality of electricallydetonable explosive charges located at the remote subterranean formationfor establishing communication between the productive subterraneanformation and the interior of the easing 17. The perforating apparatus21 comprises conventional surface equipment 23 and a plurality ofdiscrete and separable gun means; such as, guns 25, 27 and 29; suspendedin the casing 17 via cable 31. A conventional lubricator 33 is providedfor insertion and running in of the guns and cable through theconventional well head,, illustrated by valve 35.

The cable 31 comprises at least two electrical conductor means,conventionally an internal conductor and a shield that serves as anelectrical common, or ground. The cable 31 is shown as being connectedto a winch 37 by way of pulley 39. The cable 31 is wound on a drum onthe winch 37 in accordance with usual practice. The electricalconductors comprising the at least two conductor means are connectedwith a direct current voltage supply source 41 by way of a selectorswitch 43. The voltage source 41 and the selector switch 43 cooperate,as illustrated in FIG. 4, to enable impressing an electrical signal ofthe desired polarity onto the conductors 45 and 47 of the cable 31.

The respective plurality of gun means are connected with the cable 31 byadapter sub 49 and cable head 51. Conventional adapter subs and cableheads may be employed. Accordingly, there is no need for furtherdetailed descripton of them herein.

Each of the gun means, such as gun 25, has a plurality of charges; afiring electrical connector means for firing the charges; isolationmeans for maintaining the charges electrically insulated prior tofiring; actuator means for effecting stepping of the firing electricalconnector means to connect the respective charges to the first conductormeans; and advancing means for advancing the actuator means of a gunmeans. The broadly recited elements will be specifically delineatedlater hereinafter with respect to FIG. 4. As illustrated in FIGS. 1-3,each gun comprises first and second modules 55 and 57. First module 55contains the firing electrical connector means, the actuator means, theisolation means and the advancing means. The second module 57 containsthe charges 53. By this modular construction the desired number of gunsmay be readily assembled in the field for a given perforating job. Thefirst module may be readily interchanged, replaced or repaired asnecessary without having to replace an entire gun.

In the first module, the firing electrical connector means includes aunidirectional conduction means for passing current of a first polarity.The firing electrical connector means is electrically connected with therespective charges 53 and with the first conductor means, such asconductor 45 in FIG. 4, and operable to connect the conductor 45 withrespective charges 53 responsive to the actuator means. The actuatormeans also includes a second unidirectional conduction means for passingcurrent of a second polarity for effecting intra-gun advancing.

The advancing means of a particular gun comprises first and secondportions for at least initially advancing the guns own actuator means,or intra-gun advancing, and a third portion for initially advancing theactuator means ofa next higher gun in the perforating apparatus 21. Thefirst portion of the advancing means is electrically connected with thefirst conductor 45 when the isolation means is maintaining the chargeselectrically insulated. The second portion is drivingly connected withthe actuator means. The third portion is electrically connectable withthe conductor means aftr, and only after, the charges in its gun meanshave been fired in normal operation such that the firing electricalconnector means of the next higher gun is moved from the isolation meansand connected with the first charge in the next higher gun after, andonly after, the charges in the lower or associated gun have been firedin normal operation. The term associated gun" as used herein means thegun that is associated with a particular charge selector assembly 125.The term lower gun as used herein in some cases includes an associatedgun.

An electrical interconnection is electrically connected with the firstand second portions of the advancing means in the bottom gun such that asignal of the second polarity will step the actuator means of the bottomgun, and only the bottom gun, so as to connect the firing electricalconnector means with the first charge in the bottom gun. Thereafter, asignal of the first polarity can fire the first charge. The advancingmeans also contains a third unidirectional conduction means to preventshort circuiting of the signal of second polarity in the event that theadvancing means in a lower gun becomes grounded.

Referring to the figures for specific construction, and particularlyFIG. 4, the selector switch 43 is illustrated as a double-pole,double-throw reversing switch; the knife terminals 59 and 61 of whichare respectively connected to the positive and negative terminals of theDC voltage supply source 41. The first conductor 45 of the cable 31 isconnected with switch terminals 63 and 69. The conductor 47 is connectedto switch terminals 67 and 65. Thus, when the switch blades are thrownto the right, as shown, first conductor 45 is positive with respect tosecond conductor 47. Conversely, when the switch blades 59 and 61 arethrown to the left, the conductor 45 is negative with respect to theconductor 47.

In this way, signals of the respective first and second polarities areproduced.

As illustrated in FIGS. 2 and 4, each of the guns carries a steppingswitch means for connecting its first and second main terminals 77 and79 sequentially with respective contacts 81 and 83 spaced around itsrespective deck means; such as, first and second decks 102 and 103. Eachstepping switch means 75 has an actuator means such as armature 87 ofsolenoid 85. The armature 87 of the solenoid has thereon a pivoted dog89 that is positioned and adapted to engage the serrations in wheel 91.Wheel 91 is connected, as indicated by dashed line 93, with movablewiper arms 95 and 97. The wiper arm 95 is electrically connected withthe first main terminal 77, which is connected with the first conductor45. The wiper arm 97 is connected with the second main terminal 79. Thewheel 91 rotates unidirectionally clockwise in response to respectivemovement of the armature 87 of the solenoid 85, and each wiper arm movessequentially to make electrical connection with the respective contacts81 and 83. As illustrated, the stepping switch means has twelve contactson each deck; ten for firing ten charges plus an ultimate andpenultimate contact. Use of all of the respective contacts is notnecessarily required, but is advantageous in allowing alternateadvancing and firing without interruption. The contacts 81, exclusive ofthe ultimate contact 81a and penultimate contact 81b, of the first deck102 are connected together; and are connected with the second mainterminal 79 of the second deck 103 via a first unidirectional conductionmeans, such as diode 99, for passing current of a first polarity forfiring the respective charges. The contacts 81 are also connected via asecond unidirectional conduction means such as diode 101 with thesolenoid 85 for passing current for a second polarity for stepping thestepping switch means 75. The contacts 83, exclusive of the ultimate andpenultimate contacts 83a and 83b, of the second deck means 103 areconnected with respective charges 53 such that the charges are firedupon the application of firing current to their respective contact.Thus, it can be seen that the firing electrical connector meanscomprises the respective interconnected contacts 81 and wiper arm 95 ofthe first deck 102 and the wiper arm 97 and respective correlativecontacts 83. As illustrated in FIG. 2, the conductors 106 are connectedwith tabs 107 which in turn are connected respectively to those contacts81, 83 of the first and second decks 102 and 103 which are to receiveexternal connections, to main terminal 77, and to lead 153; and areshown discontinuous for clarity of illustration. The first module 55comprises the charge selector assembly and its housing 126. In themechanical arrangement of the charge selector assembly 125, FIG. 2, therespective elements are supported by threaded rods 131 screwed into ahousng 132 and carrying respective fiberglass circular supports 135.External connections from the charge selector assembly are made viacontact pins 139 whih are inserted through a sealing and insulatingblock 141, which may be Delrin. The lower ends of the contact pinsprotrude from the bottom of the block 141 and are connected, as bysoldering, to the conductors 106. The block 141 is sealingly insertedwith appropriate O-rings in the bore of housing 132. The housing 132 isscrewed into the internal threads of the housing 126 of shot selectorassembly 125. The contact pins 139 are adapted at their upper ends toreceive respective conductors for external connections. The respectiveconductors are inserted in a transverse opening in a respective contactpin 139 and insulated and secured on the pin by means of a boot 143. Theelectrically operated elements and their electrical interconnections aresealingly emplaced within the charge selector assembly 125 with theillustrated appropriate machined fittings and O-rings so as to preventthe invasion of borehole fluids; such as, aqueous fluids that couldcause malfunctioning. As illustrated, each charge, too, is protectedagainst invasion of borehole fluids. For example, as illustrated inFIGS. 2 and 4, the conductor 105 from the charge selector assembly 125of the next higher gun is connected via respective sealed contact pin139, and fluidproof seal 109 with the first charge 53a behind chargeport plug 111.

In fact, as illustrated in FIGS. 1 and 3, each charge 53 is connectedthrough respective sealed contact pin 139 and via its respectiveconductor 113 by way of its seal 115 in respective tandem subs 119thatjoin respective charge sections 121. Each section 121 houses acharge 53; and the respective tandem subs enable making up as manycharges as desired in a single gun. I have found it advantageous, forexample, to employ ten charges requiring ten charge sections 121 andnine tandem subs 119, FIG. 1. The selector top 123, FIG. 2, for the shotselector assembly 125 serves for connecting the bottom charge, asillustrated in FIG. 2. The respective male ends of the tandem subs areinserted within conforming machined recesses of the adjacent sectionswith appropriate seals, such as O-rings 127, and retained in place byretainers, such as Allen head set screws 129. Similarly, the respectivemale ends of the selector top 123 and the charge selector assembly 125are inserted within respective recesses and held by the set screws 129.

Referring to FIGS. 1 and 4, the first conductor 45 serves as acorrelative conductor coming into the top gun 25. Each of the guns havea first conductor means such as conductor 147 that is serially connectedwith the first correlative conductor coming into the gun means and withthe first main terminal 77 of the first deck 102. Each gun also has asecond conductor means such as conductor 149 that is serially connectedwith the penultimate contact 81b on the first deck and with a secondcorrelative conductor when there is a next higher gun. The conductor 149serves as a third portion of the advancing means. Since there is no nexthigher gun after the top gun, there is no need for the third portion ofthe advancing means; and the conductor 149 is left floating, orelectrically discontinuous, in the top gun. Each gun also has third andfourth conductor means, such as conductors 151 and 153, that definerespective first and second correlative conductors for electricalinterconnection between an upper gun and an adjacent lower gun. Thefirst and second portions of the advancing means comprise the third andfourth conductors 151 and 153. The third conductor 151 is connected withthe ultimate contact 81a on the first deck 102, and thus provideselectrical continuity when the wiper arm 95 is on the contact 81a,serving as the isolation means. The fourth conductor 153 is connectedwith the solenoid 85 via a third unidirectional conduction means such asdiode 155 for passing current of a second polarity for stepping thestepping switch means 75 from the penultimate contact 81a of the lowergun 27. The second portion of the advancing means also includes diode155. It can be seen that after, and only after, the charges in a lowergun 27, FIG. 4, have been fired in normal operation, the penultimatecontact 81b and second conductor 149 of gun 27, and the fourth conductor153 of the gun 25 connect the solenoid 85 of gun 25 with the firstconductor 45 for advancing the stepping switch means of gun 25. Diode155 serves to electrically isolate the solenoid in event that there is ashort circuit in the conductors of the associated (gun which may occurduring the firing of the charges therein) such that the solenoid 85 ofthe associated gun would otherwise be short circuited. Specifically, thediode 155 will not pass stepping current into the short circuitedelectrical conductors, and consequently, the solenoid 85 of theassociated gun will operate when the signal is passed through respectivesecond diode 101, regardless of what has transpired in the associatedgun.

An electrical interconnection 157 is connected with the third and fourthconductors 151 and 153, preferably at the well site. Thus, the first andsecond portions of the advancing means are connected by the electricalinterconnection 157 in the bottom gun. The electrical interconnection157 thus electrically connects the correlative conductors on the bottomgun such tat a signal of the second polarity will step the actuatormeans and, consequently, the stepping switch means of the bottom gunonly; and connect the respective first contacts on the respective decks102 and 103 with respective first and second main terminals 77 and 79.Thereafter, a signal of the first polarity can fire the charge connectedwith the first contact on the second deck 103.

In operation, the perforating apparatus 21 is connected as describedhereinbefore and the plurality of discrete and separable gun means arelowered, via cable 31, into the borehold 11 for perforating the casing17 opposite the productive formation 15. As illustrated, there are tencharges 53 connected into each respective gun means and electricallyconnected with respective contacts 83 on the second deck 103 of therespective stepping switch means 75. The charges are maintainedelectrically isolated by the respective wiper arms being disposed oncontact 81a. Thus, the ultimate contacts 81a and 83a serve as initialisolation contacts. Moreover, the contact 810 and the respectiveconductors 151 and 147 effect electrical continuity of the firstconductor 45 throughout the serially connected guns. The mechanicaljoinder of the respective subs and housing of the guns effect electricalcontinuity of second conductor 47, illustrated by the ground symbol. Thecharges are grounded to the gun casings for firing, without requiring aseparate electrical return.

The modular construction illustrated and described hereinbeforefacilitates assembly of as many guns as desired at the well site andalleviates the necessity for careful preparing of individualized customperforating apparatus at a central location. Moreover, greater safety iseffected since the respective elements may be carried to the well siteseparately and interconnected at the well site. The modular constructionalso facilitates replacement of faulty selector assemblies withoutrequiring discarding an entire gun.

Once the guns are emplaced in the well, movement of the selector switch43 to produce a signal of the desired polatity will effect, by way ofelectrical interconnector 157, advancing of the bottom relay 85 toadvance the wiper arms 95 and 97 onto their respective first contacts.Specifically, the movement of the wiper arm 95 effects removal of theisolation means and electrically connects the first charge with thefirst conduc tor 45, by way of diode 99 and wiper arm 97. Thereafter,the selector switch 43 is moved in the opposite direction to provide thefiring signal of the desired first polarity which is passed by diode 99to fire the first charge. After the first charge is fired, the selectorswitch is moved in the opposite direction to provide a signal of thesecond polarity. Diode 99 blocks the signal of the second polarity. Thesignal of second polarity is conducted via diode 101 to solenoid 85 toadvance the stepping which to the second contact. Thereafter, theselector switch 43 is moved in the opposite direction to provide asignal of the first polarity to fire the second charge 53. The alternatemovement of the stepping switch effects respective firing and advancingof the stepping switch means 75 until all of the charges have been firedin normal operation. After the tenth charge has been fired, the nextsignal of the second polarity will advance the wiper arm 95 to thepenultimate contact 8112 which serves as a final isolation contact withrespect to the effects electrical interconnection via conductors 149 and153 and diode 155 with the solenoid 85 to effect advancement of thestepping switch means 75 of the upper gun 25. Consequently, the wiperarms 95 and 97 of the upper gun 25 are advanced to their first contacts.Movement of the selector switch in the opposite direction to produce asignal of the first polarity will fire the first charge 53:: of theupper gun 25. Similar sequential and alternate stepping and firing ofcharges will fire all of the charges in the upper gun 25; and theneffect advancement of the stepping switch means of any higher gun, asdescribed hereinbefore.

Although the stepping switch means 75 has been illustrated as amechanical stepping switch employing solenoid 85 for its actuator meansto advance wiper arms 95 and 97, any other stepping switch or switchingdevice that can be programmed to switch in a sequential manner may beemployed. For example, cross bar switches; other random access switchingdevices; solid state switching devices; logic elements; ring counters;or any combination thereof can be employed as the stepping switch meansas long as they can be programmed to switch in the described sequentialmanner and provide the described functions.

The details of the physical interconnection of the respective elementsherein have been treated only briefly since they are within the purviewof those skilled in the art and do not require elaborate and detaileddescription. Likewise, the emplacement of the respective charges, andtheir alignment and protection by alignment washers and port plugs havebeen treated summarily, since they are within the skill of thoseconversant with this art.

From the foregoing descriptive matter it can be seen that this inventionprovides the objects delineated hereinbefore. Specifically, it providesthe following desirable features: (1) the guns are fired, beginning withthe lowest or bottom charge and progressing upwardly, in accordance withthe accepted desirable technique; (2) the risk of damaging necessaryelectrical conductors due to guns being fired adjacent such conductorsis eliminated by the unique disconnect system embodied in the seriesconnection of the individual selector assemblies; that is, the shortcircuiting caused by damage in a lower gun is made inconsequential bythe isolation effected by the third diode (3) each set of selectivelyfired charges can be fired by a single charge selector assembly; eachgun comprises first and second modules such that the second modulecontaining the charges can be preassembled at a convenient place, suchas a loading shop, and the first module containing the charge selectorassembly readily joined thereto; these sets of guns can then be easilytransported to the well site where any number of guns can be connectedin series by splicing two electrical conductors between each set andmechanically connecting the sets as described; (4) the charge selectorassembly is constructed as a modular unit and requires no permanentelectrical connections and can be quickly removed for replacement in thefield; (5) the system is operable with conventional single conductorwire line cable; (6) any number of selector assemblies can be connectedin series and operated without additional power require ments; and (7)the isolation means of the respective guns retain the chargeselectrically isolated until the charges in a given gun are desired to befired; this latter feature providing greater safety.

Although the invention has been described with a certain degree ofparticularity, it is understood that the present disclosure is made onlyby way of example and that numerous changes in the details ofconstruction and the combination and arrangement of parts may beresorted to without departing from the spirit and the scope of theinvention. For example, many equivalents will occur to those skilled inthe art once Applicants invention has been delineated.

What is claimed is:

1. ln apparatus for selectively detonating from an operating location aplurality of electrically detonatable explosive charge means located ata remote location and having:

a. first and second conductor means for conducting electrical signalsextending from the operating location to the remote location, anddefining a first correlative conductor and electrical common at theremote location;

b. means at said operationg location connected to said first and secondconductor means for applying electrical signals of the desiredpolarities to said first and second conductor means;

the improvement comprising:

c. a plurality of discrete and separable gun means for carrying anddetonating a predetermined number of said charges, said gun means beingdisposed at the remote location, each said gun means carrying, inaddition to the charges, a charge selector assembly comprising:

i. a stepping switch means for connecting first and second mainterminals sequentially with respective contacts spaced around respectivefirst and second deck means of the stepping switch means, said steppingswitch means having actuator means for advancing and effectingrespective connections in response to an electrical signal; saidstepping switch means having respective first and second main terminalsof said first and second deck means connected with respective ultimatecontacts before firing; said ultimate contacts being electricallyisolated from contacts that are connected with respective charges; saidfirst and second deck means having respective first and secondpenultimate contacts that are also electrically isolated from thecontacts connected with said charges; said first penultimate contact ofsaid first deck means being connected with a second conductor means, asrecited in element (c), (ii), hereinafter, for advancing a next upperguns stepping switch means only after said first penultimate contact isconnected with said first main terminal; a plurality of said contacts,exclusive of the ultimate and penultimate contacts, of the second deckmeans being electrically connected with respective charges such thatsaid charges are fired upon the occurrence of firing current on theirrespective contact; a plurality of the same number of contacts,exclusive of the ultimate and penultimate contacts, of the first deckmeans being connected together, being electrically serially connectedwith the second main terminal of the second deck means and thence viarespective said contacts of said second deck means and charges with saidelectrical common; the electrical connection with said second mainterminal being via a first unidirectional conduction means that isconnected for conduction in the forward direction for passing current ofa first polarity through respective said charges to electrical commonfor firing said respective charges, said plurality of said connectedtogether contacts of said first deck means also being connected withsaid actuator means via a second unidirectional conduction means that isconnected for conduction in the forward direction for passing current ofa second polarity for energizing said actuator means to advance saidstepping switch means;

ii. a first conductor means being serially connected with a firstcorrelative conductor coming into said gun means and with said firstmain terminal of said first deck means; and a second conductor meansbeing serially connected with said penultimate contact on said firstdeck and with a second correlative conductor on any higher guns means;

iii third and fourth conductor means defining first and secondcorrelative conductors for electrical interconnection; said thirdconductor means being connected also with said ultimate contact on saidfirst deck means; and said fourth conductor means being connected alsowith said actuator means via a third unidirectional conduction meansthat is connected for conduction in the forward direction for passingcurrent of the second polarity for energizing said actuator means; and

d. an electrical interconnection electrically connecting the first andsecond correlative conductors on the bottom gun means so that a signalof the second polarity will energize said actuator means andconsequently step said stepping switch means of the bottom gun only, andconnect the respective first contacts on the respective first and seconddeck means with the respective first and second main terminals so that,thereafter, a signal of the first polarity will fire the chargeconnected with said first contact; whereby sequential signals ofalternate polarity will effect advancing of 65 said stepping switchmeans to and firing of all of said charges in a lower gun means and thenadvance the stepping switch means of the next higher gun after, and onlyafter, the stepping switch means of the said lower gun means has beenadvanced beyond the last charge thereof and to its penultimate contactposition.

2. The apparatus of claim 1 wherein each said gun means comprises firstand second modules, said first module containing said charge selectorassembly, and said second module contains said charges, whereby thedesired number of gun means may be readily joined in the field to makeup the requisite assembly for a given perforating job, and said firstmodule may be readily replaced if defective without having to replace anentire gun means.

3. The apparatus of claim 1 wherein each said third and fourth conductormeans and said ultimate contact of a lower gun means are necessary onlyfor advancing its stepping switch means to connect its first charge withthe first conductor means, and a fault in the circuit of its third andfourth conductor means thereafter is inconsequential to normal operationof said gun means and any higher gun means.

4. Apparatus for selectively detonating from an operating location aplurality of electrically detonatable explosive charges located at aremote location comprising:

a. first and second conductor means extending from the operationlocation to the remote location;

b. a plurality of discrete and separable gun means for carrying anddetonating a predetermined number of said charges, said gun means beingdisposed at the remote location; each said gun means having: i. aplurality of charges;

ii. a firing electrical connector means for firing the charges, saidfiring electrical connector means including respective first and seconddeck means, input terminals, and output contacts, with output contactson said first deck means being serially connected with the inputterminal of said second deck means via a unidirectional conduction meansthat is connected for conduction in the forward direction for passing asa first signal current of a first polarity; said firing electricalconnector means being connected with said first conductor means andoperable to connect it to respective said output contacts on said seconddeck means and thence via respective said charges to electrical common,said output contacts being connected with respective said charges forfiring;

iii. isolation means that includes initial and final isolation contactsthat are electrically isolated from said contacts of said firingelectrical connector means for maintaining said charges electricallyisolated prior to firing said charges regardless of the magnitude of thevoltage effecting said first signal and that are connected respectivelywith said first and third portions of said advancing means, as recitedin b.v. hereinafter, for advancing its own actuator means initially andadvancing the actuator means of the next higher gun means only aftersaid firingelectrical connector means has been advanced through all ofits contacts that are connected with respective charges in its gunmeans;

iv. actuator means for effecting stepping of said firing electricalconnector means;

v. advancing means for advancing the actuator means of a gun means; saidadvancing means electrically connecting said actuator means with saidfiring electrical connector means via a second unidirectional conductionmeans that is connected for conduction in the forward direction forpassing as a second signal current of a second polarity and not passingsaid first signal; said advancing means also comprising first and secondportions for initially advancing its own actuator means and a thirdportion for initially advancing the actuator means of the next highergun; said first portion of said advancing means being electricallyconnected with said first conductor means via said initial isolationcontact when said isolation means is maintaining said chargeselectrically isolated; said second portion being drivingly connectedwith said actuator means; and said third portion being connected withsaid final isolation contact of said first deck means of said firingelectrical connector means so as to be electrically connected with saidfirst conductor means after, and only after, the actuator means in itsgun means has advanced said firing electrical connector means beyond thelast charge connected thereto such that the firing electrical connectormeans of the next higher gun is moved from its isolation means andconnected with its first charge;

c. an electrical interconnection electrically connected with the firstand second portions of the advancing means in the bottom gun such taht asecond signal of said second polarity will step said actuator means ofthe bottom gun, and only the bottom gun, so as to connect the firingelectrical connector means with the first charge therein; and,thereafter, a first signal of said first polarity will fire the firstcharge; and

d. means at said operating location connected to said first and secondconductor means for applying the first and second signals to said firstand second conductor means;

whereby sequential first and second signals of alternate polarity willeffect advancing of said actuator means to and firing of all of saidcharges in a lower gun means and then advance the actuator means of thenext higher gun means after, and only after, the actuator means and saidfiring electrical connector means of said lower gun means has beenadvanced beyond the last charge thereof.

5. The apparatus of claim 4 wherein said first and second portions ofsaid advancing means are necessary only for moving said firingelectrical connector means from the isolation means and onto the contactconnected with the first charge and failure of said first and secondportions thereafter is inconsequential to normal operation of the gunmeans and respective other higher gun means.

6. The apparatus of claim 5 wherein said third portion of said advancingmeans contains a third unidirectional conduction means connected forconduction in the forward direction to prevent short circuiting saidsecond signal of said second polarity in the event the advancing meansin the lower gun means is grounded.

7. The apparatus of claim 41 wherein each said gun means comprises firstand second modules,

said first module containing said firing electrical connector means,said actuator means, said isolation means and said advancing means; and

said second module containing said charges; whereby the desired numberof gun means may be readily joined in the field to make up the requisiteassmbly for a given perforating job and said first module may be readilyreplaced if defective without having to replace an entire gun means.

1. In apparatus for selectively detonating from an operating location a plurality of electrically detonatable explosive charge means located at a remote location and having: a. first and second conductor means for conducting electrical signals extending from the operating location to the remote location, and defining a first correlative conductor and electrical common at the remote location; b. means at said operationg location connected to said first and second conductor means for applying electrical signals of the desired polarities to said first and second conductor means; the improvement comprising: c. a plurality of discrete and separable gun means for carrying and detonating a predetermined number of said charges, said gun means being disposed at the remote location, each said gun means carrying, in addition to the charges, a charge selector assembly comprising: i. a stepping switch means for connecting first and second main terminals sequentially with respective contacts spaced around respective first and second deck means of the stepping switch means, said stepping switch means having actuator means for advancing and effecting respective connections in response to an electrical signal; said stepping switch means having respective first and second main terminals of said first and second deck means connected with respective ultimate contacts before firing; said ultimate contacts being electrically isolated from contacts that are connected with respective charges; said first and second deck means having respective first and second penultimate contacts that are also electrically isolated from the contacts connected with said charges; said first penultimate contact of said first deck means being connected with a second conductor means, as recited in element (c), (ii), hereinafter, for advancing a next upper gun''s stepping switch means only after said first penultimate contact is connected with said first main terminal; a plurality of said contacts, exclusive of the ultimate and penultimate contacts, of the second deck means being electrically connected with respective charges such that said charges are fired upon the occurrence of firing current on their respective contact; a plurality of the same number of contacts, exclusive of the ultimate and penultimate contacts, of the first deck means being connected together, being electrically serially connected with the second main terminal of the second deck means and thence via respective said contacts of said second deck means and charges with said electrical common; the electrical connection with said second main terminal being via a first unidirectional conduction means that is connected for conduction in the forward direction for passing current of a first polarity through respective said charges to electrical common for firing said respective charges, said plurality of said connected together contacts of said first deck means also being connected with said actuator means via a second unidirectional conduction means that is connected for conduction in the forward direction for passing current of a second polarity for energizing said actuator means to advance said stepping switch means; ii. a first conductor means being serially connected with a first correlative conductor coming into said gun means and with said first main terminal of said first deck means; and a second conductor means being serially connected with said penultimate contact on said first deck and with a second correlative conductor on any higher guns means; iii. third and fourth conductor means defining first and second correlative conductors for electrical interconnection; said third conductor means being connected also with said ultimate contact on said first deck means; and said fourth conductor means being connected also with said actuator means via a third unidirectional conduction means that is connected for conduction in the forward direction for passing current of the secOnd polarity for energizing said actuator means; and d. an electrical interconnection electrically connecting the first and second correlative conductors on the bottom gun means so that a signal of the second polarity will energize said actuator means and consequently step said stepping switch means of the bottom gun only, and connect the respective first contacts on the respective first and second deck means with the respective first and second main terminals so that, thereafter, a signal of the first polarity will fire the charge connected with said first contact; whereby sequential signals of alternate polarity will effect advancing of said stepping switch means to and firing of all of said charges in a lower gun means and then advance the stepping switch means of the next higher gun after, and only after, the stepping switch means of the said lower gun means has been advanced beyond the last charge thereof and to its penultimate contact position.
 2. The apparatus of claim 1 wherein each said gun means comprises first and second modules, said first module containing said charge selector assembly, and said second module contains said charges, whereby the desired number of gun means may be readily joined in the field to make up the requisite assembly for a given perforating job, and said first module may be readily replaced if defective without having to replace an entire gun means.
 3. The apparatus of claim 1 wherein each said third and fourth conductor means and said ultimate contact of a lower gun means are necessary only for advancing its stepping switch means to connect its first charge with the first conductor means, and a fault in the circuit of its third and fourth conductor means thereafter is inconsequential to normal operation of said gun means and any higher gun means.
 4. Apparatus for selectively detonating from an operating location a plurality of electrically detonatable explosive charges located at a remote location comprising: a. first and second conductor means extending from the operation location to the remote location; b. a plurality of discrete and separable gun means for carrying and detonating a predetermined number of said charges, said gun means being disposed at the remote location; each said gun means having: i. a plurality of charges; ii. a firing electrical connector means for firing the charges, said firing electrical connector means including respective first and second deck means, input terminals, and output contacts, with output contacts on said first deck means being serially connected with the input terminal of said second deck means via a unidirectional conduction means that is connected for conduction in the forward direction for passing as a first signal current of a first polarity; said firing electrical connector means being connected with said first conductor means and operable to connect it to respective said output contacts on said second deck means and thence via respective said charges to electrical common, said output contacts being connected with respective said charges for firing; iii. isolation means that includes initial and final isolation contacts that are electrically isolated from said contacts of said firing electrical connector means for maintaining said charges electrically isolated prior to firing said charges regardless of the magnitude of the voltage effecting said first signal and that are connected respectively with said first and third portions of said advancing means, as recited in b.v. hereinafter, for advancing its own actuator means initially and advancing the actuator means of the next higher gun means only after said firing electrical connector means has been advanced through all of its contacts that are connected with respective charges in its gun means; iv. actuator means for effecting stepping of said firing electrical connector means; v. advancing means for advancing the actuator means of a gun means; said advancing meanS electrically connecting said actuator means with said firing electrical connector means via a second unidirectional conduction means that is connected for conduction in the forward direction for passing as a second signal current of a second polarity and not passing said first signal; said advancing means also comprising first and second portions for initially advancing its own actuator means and a third portion for initially advancing the actuator means of the next higher gun; said first portion of said advancing means being electrically connected with said first conductor means via said initial isolation contact when said isolation means is maintaining said charges electrically isolated; said second portion being drivingly connected with said actuator means; and said third portion being connected with said final isolation contact of said first deck means of said firing electrical connector means so as to be electrically connected with said first conductor means after, and only after, the actuator means in its gun means has advanced said firing electrical connector means beyond the last charge connected thereto such that the firing electrical connector means of the next higher gun is moved from its isolation means and connected with its first charge; c. an electrical interconnection electrically connected with the first and second portions of the advancing means in the bottom gun such taht a second signal of said second polarity will step said actuator means of the bottom gun, and only the bottom gun, so as to connect the firing electrical connector means with the first charge therein; and, thereafter, a first signal of said first polarity will fire the first charge; and d. means at said operating location connected to said first and second conductor means for applying the first and second signals to said first and second conductor means; whereby sequential first and second signals of alternate polarity will effect advancing of said actuator means to and firing of all of said charges in a lower gun means and then advance the actuator means of the next higher gun means after, and only after, the actuator means and said firing electrical connector means of said lower gun means has been advanced beyond the last charge thereof.
 5. The apparatus of claim 4 wherein said first and second portions of said advancing means are necessary only for moving said firing electrical connector means from the isolation means and onto the contact connected with the first charge and failure of said first and second portions thereafter is inconsequential to normal operation of the gun means and respective other higher gun means.
 6. The apparatus of claim 5 wherein said third portion of said advancing means contains a third unidirectional conduction means connected for conduction in the forward direction to prevent short circuiting said second signal of said second polarity in the event the advancing means in the lower gun means is grounded.
 7. The apparatus of claim 4 wherein each said gun means comprises first and second modules, said first module containing said firing electrical connector means, said actuator means, said isolation means and said advancing means; and said second module containing said charges; whereby the desired number of gun means may be readily joined in the field to make up the requisite assmbly for a given perforating job and said first module may be readily replaced if defective without having to replace an entire gun means. 